Magnetically responsive powder applicator



July 15, 1969 G. R. ANDERSON 3,455,276

MAGNETIGALLY RESPONSIVE POWDER APPLICATQR Filed May 23, 1967 25 fig INVENT OR.

United States Patent 3,455,276 MAGNETICALLY RESPONSIVE POWDER APPLICATORGlenn R. Anderson, Minneapolis, Minn., assignor to Mmnesota Mining andManufacturing Company, St. Paul, Minn., a corporation of Delaware FiledMay 23, 1967, Ser. No. 640,720

Int. Cl. Bb 5/02 U.S. Cl. 118-637 13 Claims ABSTRACT OF THE DISCLOSUREAn applicator for magnetically responsive, finely divided particulatematerial comprising a magnetizable shaft, a number of elongate magneticmembers disposed in an annular array about and extending along saidshaft in close fitting relation with the radially inner and outersurfaces of adjacent members having opposite polarity, a non-magneticsleeve disposed about the periphery of said array, and means affordingrelative rotation between said sleeve and said members.

This invention relates to an applicator for use in presentingmagnetically responsive, finely divided particles against the surface ofan article for application thereto.

The present invention is particularly useful in applying pigmentedparticulate material to an article to develop an image thereon. Oneexample of such use is in develop ing imagewise a differentiallyconductive pattern formed by projecting a light image on aphotoconductive web. The photoconductive web being positioned between aninsulative layer, backed by an electrode, and a second electrodecontacting the particulate or powder which is in electrically conductivecontact between the second electrode and the photoconductive web.

Various patents have issued on devices for applying developers, but suchdevices have had limited success at applying an even deposition of theparticulate material or developer powder on an image bearing member witha width of eight and one-half inches to thirteen inches.

Some of the previously known devices which include the use of polarizedmembers or magnetic field-producing members are shown in U.S. LettersPatent Nos. 3,152,- 924 and 3,176,652. The first of these patenteddevices uses a plurality of angularly spaced magnets set in anonmagnetic core with a plurality of short magnets aligned axially alongthe core in end-to-end relation to achieve a desired length for thedevice and with the magnets aligned so that corresponding poles on theradial edge of the magnets are facing or confronting one another. Ateach joint or area where the magnets butt together'the strength of fieldgradiant falls off; also, each magnet has a bit different strength. Allof these factors result in an uneven buildup of powder on the surface ofthe sleeve.

To overcome this the patentees promote the idea of rotating the magnetsand the non-magnetic outer sleeve in the same direction but at differentspeeds; thus the magnets shift their position with respect to the sleeveand tend to keep a uniform deposit of powder forming the brush on thesleeve. This applicator or brush is therefore considered to be undulycomplicated and, when used with powders which comprise magneticparticles coated with pigmented resin or resins, the results areunsatisfactory.

The device described in the second patent, No. 3,176,- 652, particularlywith reference to FIGURE 3 thereof, employs a fixed magnetic memberwhich can be generally cylindrical in shape but which is formed withaxially extending alternating flutes and ribs with each rib constitutinga magnetic pole of a polarity opposite to that of the next adjacent rib.This spacing between poles of op- 3,455,276 Patented July 15, 1969posite polarity, while providing a magnetic field which varies directionaround the periphery, produces areas be tween the ribs having a reducedfield. Consequently the amount of magnetic material held on the sleeveand the powder movement are decreased because the field varies with weaktangential magnetic field being present opposite the flutes. Thisdeficiency was attempted to be cured by the use of a rough exteriorsurface on the sleeve. Also, since it is very difficult to forma strongmagnetic member in this Way, magnetized with different adjacent poles,thisstructure is not satisfactory commercially or functionally. Both ofthese earlier devices thus fall short of having the capability ofdeveloping an image of uniform density.

The device of the present invention affords an applicator having auniform field along its length and strong fields around itscircumference.

The present invention provides an applicator for applying to a widesurface a dimensionally uniform deposition of magnetically responsiveparticulate material.

In practicing the present invention a plurality of magnetic members,which are formed preferably of oriented anisotropic permanent magnetmaterial dispersed in a nonmagnetic immobilizing matrix, are disposed ina circular array about a core formed of a high magnetic permeability andlow loss such as soft iron and a relatively rotatable non-magneticsleeve which supports the particulate image-forming material to be movedfrom a hopper to engaging relation with an image carrying surface.

The novel features and advantages of the present invention will becomemore apparent to those skilled in the art after reading the followingdetailed description which refers to the accompanying drawing wherein:

FIGURE 1 is a vertical sectional view of an applicating roller formed inaccordance with the present invention;

FIGURE 2 is a diagrammatic view showing the roller of the presentinvention in cross-section and its relation to other elements in acoating assembly;

FIGURE 3 is a perspective view illustrating one magnetic member;

FIGURE 4 is a graph showing the magnitude of the radial and tangentialcomponents of the circumferential magnetic field; and

FIGURE 5 is a netic field.

Referring now to the drawing, there is shown in FIG- URES 1 and 2 adeveloping assembly comprising an applying roll assembly 10 adjustablysupported between suitable insulated side frame members 11 and 12. Theassembly 10 comprises a core or shaft 13 formed of a material having ahigh magnetic permeability and low loss, e.g. soft iron, supported atopposite ends in the frame members. Positioned about the shaft 13 are aneven number of magnetic members 14 and 15, which will be described ingreater detail hereinafter. The members 14 graph showing thelongitudinal magand 15 are positioned between a fixed washer 16 and aclamping washer 17. Rotatably mounted relative to the shaft 13, as bybearing mounted end caps 18 and 19, is a non-magnetic cylindrical sleeve20 formed of a material which will not shield the magnetic field frommembers 14 and 15. On each end of sleeve 20 is a drive ring 21 againstwhich and in driving contact therewith are drive discs 22 supported by adriven shaft 23. Shaft 23 is journalled and adjustably mounted in theframe members 11 and 12 and has a drive pulley 24 on one extended endthereof which may be suitably driven from a belt 25 from a motor (notshown).

As desired in some copying applications, the applicating roll shouldserve as an electrode; therefore it is desired to connect the sleeve 20to a source of electrical potential; and in the illustrated embodiment aconnector 26 is attached to the shaft 13, to which a lead from a sourceof potential may be coupled. The sleeve 20 is electrically connected tothe shaft 13 by a sliding leaf 27 of U-shaped resilient conductivematerial. The sleeve in this example is preferably formed of aluminumbut could be formed of another non-magnetic material such as glass withan electrically conductive, non-magnetic surface coating.

The roll assembly 10, in operation, is positioned above a tray 30,mounted between the side frame members 11 and 12 and positioned forparallel aligned spaced relation to a rotating drum surface asillustrated at 31 or to a linear or convexly supported moving belt orweb. In any instance if the relatively moving surface 31 is to be coatedit carries an undeveloped image pattern to which is to be applied aneven coating of particulate image-forming magnetically responsivematerial hereinafter referred to'as powder 33, which may be supplied tothe roll assembly from a supply disposed in the hopper-like tray 30.

The tray 30 has an adjustable doctor blade 34 mounted along a forwardupturned lip which permits spatial adjustment relative to the outersurface of sleeve 20. In operation, depending on how compressed or howmuch powder is desirable at the nip area between the sleeve 20 andsurface 31, the doctor blade 34 may be adjusted between 0.010 inch and0.05 inch. The position of the sleeve 20 is also adjustable toward andaway from the surface 31 to afford light contact between the powder 33and the surface 31 or some compressive pressure on the powder at theinterface between the sleeve and the surface. Suitable means, such asslots in frame members 11 and 12 and pivoted mounting brackets, may beprovided as illustrated in the drawing to permit movement of the shafts13 and 23 relative to the surface to be coated; and suitable means, suchas a screw adjusted lever arm keyed to shaft 13, permits rotatableadjustment of shaft 13. This adjustment of shaft 13 allows accuratepositioning of either a radical edge to be normal to the surface to becoated or permits the rotation of shaft 13 to position the center of amagnetic member 14 or 15 nearest the surface to be coated.

The magnetic members 14 and 15 are alternately magnetically polarizedelongate members which are generally shaped as sectors of a ring orsectors of a hollow cylinder having radially inner faces 35 concavelycurved and convex radially outer surfaces 36 joined by radiallyextending edge walls 37. The shape of the members result in somevagaries in the dimensions and, although the members generally contacteach other, a slight gap may exist in the array between one or moremembers and not disturb the performance. The members 15 are polarized tohave a different magnetic pole on the outer surface than on the innerface; for example, the north pole indicated at N is on the outer surface36, and the south pole indicated at S is along the inner face 35, Themembers 14 would be oppositely polarized with N on the inner face and Salong the outer surface.

The members 14 and 15 are formed by extrusion of a non-magnetic matrixwhich may be a resinous or plastic composition, an elastomericsemi-solid, or viscous liquid, capable of hardening, setting or beingcured to a solid state in which is evenly dispersed anisotropic ferritedomain-sized particles, which particles are capable of achievingphysical orientation when acted upon by internal shear stresses.Examples of the particles are certain fine grain permanent magnetmaterials particularly the ferrites of barium, lead and strontium whichare easily magnetized to saturation. The matrix may be natural rubberwith compound agents, plasticizers, vulcanizing agents, and the like toprovide the hardness of the matrix desired, or may be a thermoplastic orthermo-setting material, as for example polyvinyl chloride. Preferablythe ferrite particles are oriented such that each particle (asillustrated diagrammatically in FIGURE 3 at 40) is positioned with itsmagnetic poles positioned radially relative to each other.

An even number of the wedge-shaped members 14 and 15 are alternatelyplaced in a circular array about each member and extends axially alongthe shaft 13 for the length of application desired. The members 14 and15 provide, with a 1 to 1 ratio between the radial dimension and thecircumferential dimension, a surprisingly high flux density and, in thepreferred annular array, provide a circumferential field with strongradial and tangential components. In FIGURE 4 the fiux density about thearray of magnetic members 14 and 15 is plotted in gauss with the radialfield component plotted in solid lines and the tangential fieldcomponent plotted in dotted lines. The maximum radial field exists alonga radial line bisecting the magnetic members, and the plot illustrates aflux density at the poles of 500 gauss. An optimum design is between 500and 750 gauss at the poles. The tangential flux density peaks betweenthe magnetic members and is illustrated on the plot at 300 gauss.

FIGURE 5 shows a graph along the length of the magnetic members andillustrates the readings above one pole as it is scanned from end toend. This graph'illustrates the uniformity of the magnetic fi'eld alongthe entire length of the magnetic members and that the field falls onlyat the ends. This uniformity of field affords a very uniform powderapplication by a roll assembly constructed in accordance with thisinvention.

In operation, rotation of the sleeve 20, which sleeve has a smooth outersurface with a diameter of approximately 1.250 inches and insidediameter of 1.180 inches, with a minimum clearance about the surface ofthe magnetic members of about .005 inch, carries the developing powder33 from the tray 30 across the doctor blade 34. The powder particlesappear to tumble under the effects of the changing directions of themagnetic field and move in the direction of rotation of the sleeve 20.The powder appears as a dark stripe on the areas of the sleeve above thepoles and gray above the joint between the magnetic members. As theorientation of the ferromagnetic particles achieve a more exactingradial orientation in the matrix, the gray stripe is reduced to a line.The tumbling powder stands on the sleeve surface as tree rows and, whencarried by clockwise rotation of sleeve 20 toward the clockwise rotatingor oppositely moving surface 31, they will contact the surface to bedeposited in the desired manner.

The spacing between sleeve 20 and surface 31 relative to the spacingbetween doctor blade 34 and the sleeve will determine the amount ofpowder per unit area placed in contact with the surface 31. The uniformaxial field along the sleeve provides for uniform coverage across thesurface 31 to be coated. In most applications the surface to be coatedhas a width of from 8 /2 to 14 inches, or the width or length of copysheets.

Magnetic members formed of metallic alloys such as for example thematerials sold under the trade name Alnico cannot be produced with auniform field in lengths greater than 3 to 6" because, during the heattreatment, they warp and are unusable in this type of application. Theshort segments require them to be cemented together; and at each jointthe uniformity of the field along the axis of the roller is disruptedbecause the field falls off sharply at the ends of the segments and thesegments are not identical. The uniformity achieved by a developing rollassembly formed in accordance with the present invention appreciablyreduces the variations in powder buildup on the roller or variations indensity on the developed image.

Having thus described the present invention with reference to oneembodiment, it is realized that one skilled in the art may make certainmodifications without departing from the spirit and scope of thisinvention as defined in the pending claims.

What is claimed is:

1. An applicating roller for placing a uniform layer of magneticallyresponsive dry particulate material in contact with a surface moved pastthe peripheral surface of said roller, said applicating rollercomprising a shaft of high magnetic permeability material, a pluralityof elongate, generally sector-shaped in cross section magnetic membersformed of fine grain permanent magnet material dispersed in anon-magnetic immobilizing matrix, which members are positioned With theedges thereof generally radial and in side-by-side relation to define acircular array around said shaft, and the radially inner and radiallyouter faces of each member being arcuate with said radially inner andradially outer faces of adjacent members in said array being oppositelypolarized, a uniform non-magnetic hollow cylindrical sleeve positionedover said array of magnetic members and extending axially relative .tosaid shaft, and means for mounting said sleeve and said shaft forrelative rotation to carry a quantity of said particulate material onthe outer surface of said sleeve;

2. An applicating roller as claimed in claim 1 wherein said dispersedmaterial in the magnetic members is oriented antisotropic substantiallydomain size particles of a permanent magnet material.

3. An applicating roller as claimed in claim 1 wherein said dispersedmaterial consists of substantially domain size particles of materialselected from the class consisting of the ferrites of barium, strontiumand lead.

4. An applicating roller as claimed in claim 1 wherein eight magneticmembers form a circular array about the shaft.

5. An applicating roller as claimed in claim 1 wherein said sleeve iselectrically conductive.

6. An applicating roller as claimed in claim 1 wherein each of saidmagnetic members has an axial length of between 8 and 14".

7. A powder applicator comprising in combination:

(a) an applicating roller for applying magnetically responsive drypigmented material onto a surface moved past the periphery of saidroller, said applicating roller comprising a shaft formed of highmagnetic permeability and low loss material; a plurality of elongategenerally truncated sector-shaped magnetic members formed of ferritepermanent mag" net substantially domain sized particles oriented in anon-magnetic matrix, which members are arranged in side-by-sidecontacting relation and form a circular array about said shaft withradially outer surfaces of adjacent magnetic members having oppositepolarity; a thin-Walled hollow cylindrical sleeve formed ofnon-magnetizable material positioned about and approximate to said arrayof magnetic members; and means for mounting said sleeve and said shaftfor relative rotation, each of said magnetic members extending along asubstantial portion of said shaft and covered by said cylinder;

(b) a tray for storing a supply of a said developer material in whichsaid sleeve may come in contact; and

(c) means for rotating said sleeve and said shaft relative to each otherto carry developer material from said tray about the surface of thesleeve into contact with surface to be developed.

8. A powder applicator as claimed in claim 7 wherein said shaft andmagnet members are fixed and said sleeve is rotated about said shaft.

9. A powder applicator as claimed in claim 7 wherein said sleeve has anelectrically conductive outer surface and is connected to a source ofelectrical potential,

10. A powder applicator as claimed in claim 8 wherein said sleeve has anelectrically conductive outer surface and is connected to a source ofelectrical potential.

11. A powder applicator as claimed in claim 10 wherein means areprovided for adjusting the position of said shaft.

12. An applicator for developing an image on a surface with a pigmentedfinely divided dry magnetically responsive developer material comprisingin combination,

a tray adapted to receive sai-d developer material,

an applicating roller positioned relative to said tray for moving saiddeveloper material out of said tray, said applicating roller comprisinga shaft of high magnetic permeability material,

a plurality of elongate, generally sector-shaped in cross section,magnetic members which are formed of oriented fine grain permanentmagnet material dispersed in a non-magnetic immobilizing matrix andwhich have longitudinal edges which are generally radial and positionedwith said edges in side-by-side contacting relation to form an arcuatearray on the outer circular periphery of said shaft, said members alsohaving arcuate radially inner and radially outer faces with saidradially inner and radially outer faces of adjacent members in saidarray being oppositely polarized, and

a uniform non-magnetic hollow cylindrical sleeve positioned over saidarray and mounted for rotation relative to said shaft and said magneticmembers and rotatable relative to said tray,

a doctor blade adjustably mounted on an edge of said tray adjacent theperiphery of said sleeve for limiting the amount of said developermaterial which may be carried by said sleeve out of said tray uponrotation of said sleeve, and

means for rotating said sleeve.

13. An applicator as defined in claim 12 wherein a tangential magneticfield is formed between each of said adjacent magnetic members directlyabove said contacting edges where the field gradient is large, whichfield on the surface of said sleeve has a value of at least about 300gauss.

References Cited UNITED STATES PATENTS 3,040,704 6/ 1962 Bliss 118-6373,191,106 6/1965 Baermann 335-303 X 3,219,014 11/1965 Mott et al.118-637 FOREIGN PATENTS 1,417,724 10/1965 France.

1,071,697 6/ 1967 Great Britain.

PETER FELDMAN, Primary Examiner US. Cl. X.R.

